For some time, others have worked to improve the performance and reduce the adverse environmental effects of internal combustion engines. As the increased use of automobiles and trucks in the United States has offset reductions in auto emissions, legislators, regulators, the petroleum and automobile industries, and various other groups have sought new ways to address air pollution from cars and trucks. As part of that effort, these groups have increasingly focused on modification of fuels and fuel additives. Perhaps the best known fuel modification relating to air pollution control is the elimination of lead, used as an antiknock compound, from gasoline.
The 1990 amendments to the Clean Air Act contain a new fuels program, including a reformulated gasoline program to reduce emissions of toxic air pollutants and emissions that cause summer ozone pollution, and an oxygenated gasoline program to reduce carbon monoxide emissions in areas where carbon monoxide is a problem in winter. Environmental agencies, such as the United States Environmental Protection Agency (EPA) and the California Air Resources Board (CARB), have promulgated various regulations compelling many fuel modification efforts.
With respect to the oxygenated gasoline program, the most commonly used oxygenates are ethanol, made from biomass (usually grain or corn in the United States), and methyl tertiary butyl ether (MTBE), made from methanol that is usually made from natural gas. Oxygenates such as ethanol and MTBE increase a fuel's octane rating, a measure of its tendency to resist engine knock. In addition, MTBE mixes well with gasoline and is easily transported through the existing gasoline pipeline distribution network.
Both ethanol (as well as other alcohol-based fuels) and MTBE have significant drawbacks. Ethanol-based fuel formulations have failed to deliver the desired combination of increased performance, reduced emissions, and environmental safety. They do not perform substantially better than straight-run gasoline, and also increase the cost of the fuel.
Adding either ethanol or MTBE to gasoline dilutes the energy content of the fuel. Ethanol has a lower energy content than MTBE, which in turn has a lower energy content than straight-run gasoline. Ethanol has only about 67% the energy content of the same volume of gasoline and it has only about 81% of the energy content of an equivalent volume of MTBE. Thus, more fuel is required to travel the same distance, resulting in higher fuel costs and lower fuel economy. In addition, the volatility of the gasoline that is added to an ethanol/gasoline blend must be further reduced in order to offset the increased volatility of the alcohol in the blend.
Ethanol also has a much greater affinity for water than do petroleum products. It cannot be shipped in petroleum pipelines, which invariably contain residual amounts of water. Instead, ethanol is typically transported by truck, or manufactured where gasoline is made. Ethanol is also corrosive. In addition, at higher concentrations, the engine must be modified to use an ethanol blend.
Ethanol has other drawbacks as well. Ethanol has a high vapor pressure relative to straight-run gasoline. Its high vapor pressure increases fuel evaporation at temperatures above 130° Fahrenheit, which leads to increases in volatile organic compound (VOC) emissions.
Finally, although much research has focused on the health effects of ethanol as a beverage, little research has addressed ethanol use as a fuel additive. Nor has ethanol been evaluated fully from the standpoint of its environmental fate and exposure potential.
MTBE has its share of drawbacks as well. MTBE was first added to gasoline to boost the octane rating. In line with the 1990 Clean Air Act amendments, MTBE was added in even larger amounts as an oxygenate to reduce air pollution. Unfortunately, MTBE is now showing up as a contaminant in groundwater throughout the United States as a result of releases (i.e., leaking underground gasoline storage tanks, accidental spillage, leakage in transport, automobile accidents resulting in fuel releases, etc.).
MTBE is particularly problematic as a groundwater contaminant because it is soluble in water. It is highly mobile, does not cling to soil particles, and does not decay readily. MTBE has been used as an octane enhancer for about twenty years. The environmental and health risks posed by MTBE, therefore, parallel those of gasoline. Some sources estimate that 65% of all leaking underground fuel storage tank sites involve releases of MTBE. It is estimated that MTBE may be contaminating as many as 9,000 community water supplies in 31 states. A University of California study showed that MTBE has affected at least 10,000 groundwater sites in the State of California alone.
The EPA also has determined that MTBE is carcinogenic, at least when inhaled. Other unwelcome environmental characteristics are its foul smell and taste, even at very low concentrations (parts per billion). The environmental threat from MTBE may be even greater than that from an equivalent volume of straight-run gasoline. The constituents of gasoline considered most dangerous are the aromatic hydrocarbons: benzene, toluene, ethylbenzene, and xylene (collectively, BTEX). The BTEX aromatic hydrocarbons have the lowest acceptable drinking water contamination limits. Both ethanol and MTBE enhance the environmental risks posed by the BTEX compounds, apart from their own toxicity. Ethanol and MTBE act as a co-solvent for BTEX compounds in gasoline. As a result, the BTEX plume from a source of gasoline contamination containing ethanol and/or MTBE travels farther and faster than one that does not contain either oxygenate.
The BTEX aromatic compounds have relatively lower solubility in water than MTBE. BTEX compounds tend to biodegrade in situ when they leak into the soil and ground water. This provides at least some natural attenuation. Relative to the BTEX compounds, however, MTBE biodegrades at a significantly lower rate, by at least one order of magnitude, or ten times more slowly. Some sources estimate that the time required for MTBE to degrade to less than a few percent of the original contaminant level is about ten years.
Other initiatives have involved efforts to formulate a cleaner burning-reformulated-gasoline (RFG). For example, Union Oil Company of California (UNOCAL) has secured a number of U.S. patents that cover various formulations of RFG, including Jessup, et al., U.S. Pat. No. 5,288,393, for Gasoline Fuel (Feb. 22, 1994); Jessup, et al., U.S. Pat. No. 5,593,567, for Gasoline Fuel (Jan. 14, 1997); Jessup, et al., U.S. Pat. No. 5,653,866, for Gasoline Fuel (Aug. 5, 1997); Jessup, et al., U.S. Pat. No. 5,837,126 for Gasoline Fuel, (Nov. 17, 1998); Jessup, et al., U.S. Pat. No. 6,030,521 for Gasoline Fuel (Feb. 29, 2000). The UNOCAL patents specify various end points in the blending of gasoline, and purport to reduce emissions of selected contaminants: Carbon monoxide (CO); Nitric oxides (NOx); Unburned Hydrocarbons (HC); as well as other emissions.
These various problems have impaired the efficacy or cost-effectiveness of each of these various alternatives. Alcohols have not resolved the performance and emission needs for improved motor fuels. MTBE imposes unacceptable environmental (soil and groundwater) and public health problems. Reformulated gasoline has been controversial and expensive. Accordingly, there remains a substantial and unmet need for an improved gasoline formulation that enhances (or at least does not impair) performance, while reducing emissions and the environmental and public health risks from motor fuels. The fuel additive according to an embodiment of the present disclosure satisfies those needs.
Applicant previously discovered a fuel additive that was the subject of U.S. Pat. Nos. 6,319,294 and 7,491,249, herein incorporated in their entirety. This formulation, known as “MAZ,” is shown in the table below.
TABLE 1“MAZ” FormulationWeight ComponentPercent (Wt. %)1-Nitropropane 40-60%Nitroethane 10-30%Nitromethane 10-30%Toluene  2-8%Lubricant 0.5-3%
Nitroparaffins have been used in prior fuel formulations, for different engine applications, without achieving the results of the present disclosure. For example, nitroparaffins have long been used as fuels and/or fuel additives in model engines, turbine engines, and other specialized engines. Nitromethane and nitroethane have been used by hobbyists. Nitroparaffins have also been used extensively in drag racing, and other racing applications, due to their extremely high energy content.
The use of nitroparaffins in motor fuels for automobiles and trucks, however, has several distinct disadvantages. First, some nitroparaffins are explosive and pose substantial hazards. Second, nitroparaffins are significantly more expensive than gasoline—so expensive as to preclude their use in automotive and truck applications. Third, nitroparaffins have generally been used in specialized engines that are very different than gas and diesel engines. Fourth, the high energy content of nitroparaffins requires modification of the engine, and additional care in transport, storage, and handling of both the nitroparaffin and the fuel containing the additive. Further, in some fuel applications, nitroparaffins have had a tendency to gel. The high cost, and extremely high energy content of nitroparaffins, has precluded their use as an automotive and/or truck fuel. Moreover, the extreme volatility and danger of explosion from nitromethane taught away from its use as a motor fuel for automobiles and/or trucks.